2006 Expedition- Need help shops can't figure out the issue

[Jlh8485]

This all started with it having an issue wanting to crank other than that it ran fine and no light was on. In the past 6 months we have replaced a lot of parts and had a good bit of work done (I will list below). The issue we are having now that I and two shops couldn't fix is that when you go to accelerate to pass or get out on the highway to merge is that the check engine light starts blinking and then stays on and at the same time it's popping back through the intake (not spark knocking) I want to sale it due to how many issues I have had with it but don't want to do so with it still having this issue. There has been different codes that came up but some go away but the main one that keeps showing is a misfire on cylinder 3. Now there are two more codes that came up after getting it back today plus the misfire code. The shop said only other thing they could do is put autolite spark plugs in it because they read these motors have issues with a certain spark plug but it has motorcraft in it they also said that was no guarantee and that it was running fine now but on the way home we see it's got the exact same issue. We are at a loss now. Any advice?

Parts and things done:
New spark plugs
3 new coils, cylinder 3, 7, 8
New fuel pump
New fuel and air filter
New fuel rail sensor
Oxygen sensor
Throttle body assembly
New spark plugs were cleaned by 2nd shop
Combustion chamber cleaned
Exhaust checked for back pressure
Compression test
High pressure fuel rail sensor

 

[Hamfisted]

How many miles on your Expy ? What codes are you getting now ?

 

[Jlh8485]

It only has 73k miles on it. Bought it used from an elderly lady who didn't drive it much. The codes are P0300 random misfire detected, P0303 cylinder 3 misfire and P1450 unable to bleed up fuel tank vacuum. The P0300 we have seen this whole time on and off but these others we haven't seen before. I don't know if we cleared the computer if those two will stay gone or not as we have had other codes never come back after we cleared it and drove 100 miles. Thanks for any help.

 

[Gary Waugh]

I was going to suggest that worn timing chains can cause these sort of issues, but with just 78k miles, it’s unlikely to be worn timing chains. No idea what else to suggest, hope you find the cause.

 

[99WhiteC5Coupe]

Perhaps try two treatments (back-to-back tankfulls) of Techron Fuel System cleaner (per the label instructions)?

You may have one or more fuel injectors that are dirty or sticking, and causing excess fuel in the combustion chamber or are sticking and not responding properly.

 

[Vincent Vega]

For P1450 did you check the vapor canister purge valve? That can cause this problem, and other weird problems and codes. It might have been disconnected during all that recent work, so make sure it is properly hooked up and its hoses are not thrashed. With engine off, disconnect the uppermost hose on the purge valve, and its electrical connector. Start the engine. Put your finger over the hose connection that you took the upper hose off of. If you feel suction, the valve is bad and needs replacement.

 

[Mikezr]

How's it idle and drive if your just accelerating normally?

 

[mbtech2003]

Pull the valve cover and see if one of the cam followers have jumped out. Common. Under load missfire

 

[Jlh8485]

How's it idle and drive if your just accelerating normally?

It idles and drives fine normally. It only does it when you go to get out on the highway or speed up to get around someone on the highway.

 

[Wegner44]

You’ve only replaced 3 of the coils… how old are the remaining 5? I chased random misfires until I changed all the coils. Now it runs perfect. That would be my first go to. I also bought a $90 code reader and kept it with me so I could diagnose at will. That has saved me hundreds of dollars by not having to go to the shop to change out sensors or coil paks or anything basic you can do at your home.

Hope this helps!